Julia L. Rodríguez

Reactivity of NiO for 2,4-D degradation with ozone: XPS studies.

2,4-Dichlorophenoxyacetic acid (2,4-D) is usually used as a refractory model compound that requires a prolonged reaction time for mineralization. In this study, we found that nickel oxide (NiO) significantly improved 2,4-D degradation and mineralization in reaction with ozone. Other metal oxides, such as titania, silica and alumina, were also tested in this reaction, so that, the mineralization degree was almost the same for all of them (ca. 25%), whereas NiO showed more than 60% in 1h. These outstanding results led us to study in more depth the role of NiO as catalyst in the degradation of 2,4-D. For instance, the optimum NiO loading amount was 0.3 g L(-1). The catalytic ozonation showed a high stability after three reaction cycles. With the aim of identifying the surface species responsible for the high activity of NiO, besides knowing the byproducts during the degradation of 2,4-D, XPS and HPLC were mainly used as analytical tools. According to the results, the mineralization of 2,4-D was directly influenced by the adsorbed chlorate organic compounds and oxalate group onto NiO. Therefore, NiO plays a true role as a catalyst forming surface compounds which are subsequently decomposed causing an increase in the mineralization efficiency. In addition, it was possible to identify several degradation byproducts (2,4-diclorophenol, glycolic, fumaric, maleic and oxalic acids) that were included in a rational reaction pathway. It was proposed that 2,4-D elimination in presence of NiO as catalyst is a combination of processes such as: conventional ozonation, indirect mechanism (OH) and surface complex formation.

Efficient mineralization of benzoic and phthalic acids in water by catalytic ozonation using a nickel oxide catalyst

Organic acids (OAs) are usually used as refractory model compounds that require prolonged reaction time for their mineralization by different treatments. In this study, benzoic and phthalic acids in aqueous solution were significantly degraded and mineralized by catalytic ozonation in the presence of nickel oxide (NiO). For instance, only 42% mineralization was obtained by direct reaction with molecular ozone, while by catalytic ozonation 98% was achieved. These surprising results led to study in depth the role of NiO in the catalytic ozonation of both organic acids. With the aim of identifying the surface species responsible for the high activity of NiO, X-ray photoelectron spectroscopy (XPS) and high performance liquid chromatography (HPLC) were used as the main analytical tools. According to the results, the mineralization of both organic acids was directly influenced by the organic groups adsorbed onto the NiO surface. Therefore, NiO plays a relevant role as a catalyst forming complex surface compounds which are subsequently decomposed increasing the mineralization efficiency. In addition, a simplified kinetic study was conducted to characterize the effect of NiO concentration on the removal efficiency of both organic acids and the accumulation and degradation of the main byproduct (oxalic acid). These results were explained in terms of a combination of two reaction mechanisms such as conventional ozonation and indirect reaction based on ˙OH radicals.

Photocatalytic Deposition of Nickel Nanoparticles on Titanium Dioxide

Metallic nanoparticles may be tailored to obtain specific size and morphology. In this work we present the synthesis of Ni/TiO2 catalysts by a photodeposition method. Our investigation included the photochemical and photocatalytic reduction of the nickel organometallic precursor (Ni (II) acetylacetonate) over titania (Degussa P-25) support. The photo-reduction kinetics was followed by UV-Vis and the catalysts were characterized by X-ray diffraction (XRD) and transmission electron microscopy (TEM). According to the results, the photochemical reduction of the Ni precursor was only 30% at λ= 254 nm, whereas, the photocatalytic route was approximately 90 % (λ= 365 nm) yielding Ni nanoparticles with diameter ranging from 10 to 40 nm.

Recycling strategy for water contaminated with Reactive Black 5 in the presence of additives treated by simple ozonation

ABSTRACT This study presents the treatment of wastewater contaminated with Reactive Black 5 (RB5) by simple ozonation in the presence of Na2SO4, Na2CO3 (inorganic additives), and their mixture. This oxidative treatment was a single step into a wastewater recycling process. At the end of each recycle, pH variation and UV/Vis spectroscopy of the ozonated samples were analyzed. The absorbency variations were correlated with the dynamics of ozone consumption after each recycle. The quality of the treated wastewater was evaluated by the dye fixation on cotton textile samples after each cycle. The quality of dyeing process was evaluated by a novel image processing method. The image analysis results demonstrated that the mixture of salts improved the fixation of dye after each of the eight recycling procedures. The presence of Na2SO4 favored the fixation of color and Na2CO3 catalyzed the reaction between dye and fiber. Moreover, the effect of Na2CO3 dominated the additives effect over the recycling ozonation of the RB5 dye.

Ozonation of polynuclear aromatic hydrocarbons in combination with activated carbon in the presence of methanol

Abstract This work reports the study of the decomposition of three PAHs (anthracene, phenanthrene, and fluorene) in aqueous solution at different pHs (2, 7, and 11) and in the presence of methanol as a co-solvent by two different methods: conventional ozonation (O3) and O3/activated carbon (AC). The results showed that without AC, the decomposition of anthracene and fluorene proceeded mostly by molecular O3 at pHs 2 and 7. The indirect ozonation mechanism expected at basic pH was inhibited by the presence of high concentrations of methanol, which acted as a radical scavenger. The ozone consumed by the radical formation under pH >7 induced a larger decomposition reaction rate (five times) for all PAHs at acidic and neutral conditions compared with the basic ones. The presence of AC modulated the decomposition rates for all PAHs at the pHs evaluated. The latter was confirmed by the similarity among the decomposition dynamics.